Structural Design And Activity Evaluation Of Cyclic Peptides Against Drug-resistant Candida Albicans

In recent years,with the increasing drug resistance of Candida albicans,antimicrobial cyclic peptides have gradually become a new class of alternative drugs for the treatment of drug-resistant Candida albicans infections.In this paper,a series of novel antibacterial cyclic peptides were designed through the rational design principles of antimicrobial cyclic peptides.Heat shock protein 90 was selected as the target protein,and the newly designed antimicrobial cyclic peptide was molecularly docked.Molecular dynamics simulation was used to further explore the stable conformation of the antimicrobial cyclic peptide bound to the target protein,and the results of the binding free energy were used to finally determine the candidate antimicrobial cyclic peptide cyclic peptide.The 4 candidate antibacterial cyclic peptides with good results were tested for in vitro antimicrobial activity,cytotoxicity and stability;their effects on the cell membrane,cell wall and biofilm of drug-resistant albicans were further explored to determine their mechanism of action;In vivo antimicrobial activity was studied in a rat skin infection model.In this paper,four candidate cyclic peptides(A1,A2,B2,C3)were selected through rational antimicrobial cyclic peptide design,molecular docking,molecular dynamics simulation and binding free energy results.The results of in vitro antimicrobial activity experiments showed that cyclic peptides A1 and A2 had almost no activity against Candida albicans,while the MICs of cyclic peptides B2 and C3 against drug-resistant Candida albicans(28A,28D)were 64 μg/m L and MFC was 128 μg /m L,the effect is better than the positive control fluconazole(FLC).Cyclic peptide B2 and C3 had better bactericidal effect on 28 A and 28 D within 4 h,and the bactericidal effect of cyclic peptide B2 was slightly stronger than that of C3.Cyclic peptides B2 and C3 combined with FLC can act as antimicrobial synergists.The hemolytic toxicity of cyclic peptide B2 and C3 increased in a dose-dependent manner,and the hemolytic toxicity of cyclic peptide C3 at 128 μg/m L was close to 30%,which was relatively high.However,the hemolytic toxicity of cyclopeptide B2 at MFC concentration is less.The results of cytotoxicity experiments showed that the inhibition rates of cyclic peptides B2 and C3 on L929 were lower than 36% under the therapeutic dose and bactericidal dose,indicating that their effects on cell growth were relatively small.However,when the concentration of cyclic peptide B2 and C3 reached256 μg/m L,the cell proliferation inhibition rates were 78% and 77%,respectively,indicating that both have high cytotoxicity at high concentrations.The results of stability experiments show that cyclic peptide B2 still has high stability under Na Cl(36 mg/m L)and Ca Cl2(1 mg/m L),and the stability in plasma is relatively poor.Cyclic peptide B2 is safe and stable.The properties were higher than those of cyclic peptide C3.The research results of the effects of cyclic peptides B2 and C3 on cell membranes and biofilms indicated that the most likely antimicrobial mechanism of the two was to damage their cell membranes.Finally,the results of in vivo antimicrobial activity studies showed that the high-concentration cyclopeptide B2 group,the low-concentration cyclopeptide B2 group,and the Caspofungin group all had a certain effect on skin-resistant Candida albicans infection,and the Caspofungin group had a certain effect on skin-resistant Candida albicans infection.And the-high concentration of cyclic peptide B2 group and Caspofungin group have the same effect.Among the candidate cyclic peptides obtained through rational antimicrobial peptide design in this paper,cyclic peptides B2 and C3 have good antimicrobial activity against Candida albicans(especially drug-resistant Candida albicans).Compared with cyclic peptide C3,cyclic peptide B2 has stronger antimicrobial activity,higher safety and better stability.The proposed mechanism of action of the candidate cyclic peptide disrupts the fungal cell membrane.The above results not only provide a new drug candidate for the prevention and treatment of drug-resistant Candida albicans in clinical practice,but also provide a new idea for the development of drugs for the treatment of drug-resistant fungi through the design process of the antimicrobial cyclic peptide.